The technology to utilize a hydrogen storage alloy, which can store hydrogen compactly at a low pressure, as a hydrogen source of a hydrogen utilizing equipment as typified in a fuel cell is developed. Also, the development of the device, which informs of a remaining quantity of hydrogen, like a remaining indicator of a battery or a gasoline tank is advanced in parallel such that the user can know a remaining hydrogen in the hydrogen storage vessel.
For example, in Patent Literature 1, the device in which an increase in volume of the hydrogen storage alloy in a chamber via a filter is converted into an electric signal to calculate a degree of hydrogen reaction has been proposed. However, this device has such drawbacks that 1) a size of the sensor is needed to some extent, 2) it is difficult to attain a size reduction, 3) an output is easily changed depending on a direction of the vessel, 4) a volume is varied along with the progress of pulverization of the hydrogen storage alloy, and the like.
In Patent Literatures 2, 3, 4, the device in which an electrode is arranged to both ends of the hydrogen-storage-alloy filling portion and then a remaining hydrogen is sensed in response to a change of an electric resistance value has been proposed. However, in fact the obtained electric resistance value depends on a contact density between powders of the hydrogen storage alloy. Therefore, this device also has such drawbacks that an output is easily changed depending on the pulverization of the hydrogen storage alloy or the direction of the vessel, like the above device.
Also, in Patent Literature 5, the hydrogen remaining meter in which hydrogen storage alloys whose plateau pressure is different respectively are put in a vessel and stepwise changes of a pressure are regarded as changes of remaining hydrogen has been proposed. In Patent Literature 6, the hydrogen remaining meter in which pressure/temperature of a vessel are applied to a PCT characteristic diagram of the hydrogen storage alloy to calculate an amount of absorbed hydrogen has been proposed. These hydrogen remaining meters are sufficiently effective if a temperature gradient is hardly present in the overall vessel containing the hydrogen storage alloy and a hydrogen pressure is in a gas-solid equilibrium. However, in most cases the pressure/temperature are in a transient state under the actual using conditions, and thus it is very difficult to calculate a precise amount of remaining hydrogen by the above method. Also, a sensing precision of remaining hydrogen is worsened much more when the pressure enters into a plateau area. In addition, sensors for measuring a temperature and a pressure must be provided, and therefore the device is increased in space and weight.
Also, in Patent Literature 7, the device in which a strain gauge is stuck on a wall of the hydrogen storage vessel and a remaining hydrogen is sensed in response to a change of output has been proposed. The drawbacks of this device are given as two points. That is, (1) a distribution of the hydrogen storage alloy is changed when the direction of the vessel is changed and thus a strain output is also changed at the same hydrogen absorption amount, so that reproducibility of a hydrogen remaining value become worse. (2) In order to correlate a hydrogen remaining state of 0% to 100% with a strain output of the vessel wall on a one-to-one basis, an inflation stress must be applied to an inner wall of the vessel from an initial stage of absorption, so that the device cannot be implemented unless a filling density of the hydrogen storage alloy should be increased considerably high. However, a plastic deformation or a fracture of the vessel is caused without fail at such filling density of the hydrogen storage alloy. But then a range in which the hydrogen storage alloy exerts a pressure on the inner wall of the vessel is restricted in a high hydrogen capacity range when the filling density of the hydrogen storage alloy is lowered. As a result, a change of strain in an essential low hydrogen remaining range cannot be sensed.    Patent Literature 1: JP-B-1-28341    Patent Literature 2: JP-B-2-31004    Patent Literature 3: Japanese Patent No. 3624816    Patent Literature 4: JP-A-2000-97931    Patent Literature 5: JP-A-59-78902    Patent Literature 6: JP-A-2-140641    Patent Literature 7: Japanese Patent No. 3203062